HUGE formations of allied Second World War bombers did more than inflict devastation on Dresden and other German cities – they had an impact on the weather, Birmingham scientists have learned.

Experts turned to the wartime bombing raids to study the effect of thousands of aircraft on the English weather.

The missions took place at a time when skies were much less crowded than they are today, providing an opportunity to observe what difference they made to local climate.

Analysis of Met Office and military records showed a measurable impact on May 11, 1944, when 1,444 aircraft took off from airfields across south-east England into a clear sky.

Contrails from the bombers significantly suppressed morning temperature increases in areas which were heavily over-flown.

Professor Rob MacKenzie, from the University of Birmingham, who co-led the study, said: “Witnesses to the huge bombing formations recall that the sky was turned white by aircraft contrails.

“It was apparent to us that the Allied bombing of WW2 represented an inadvertent environmental experiment on the ability of aircraft contrails to affect the energy coming into and out of the Earth at that location.”

The research has been published in the International Journal of Climatology.

Aircraft contrails are formed when hot, aerosol-laden air from a plane’s engines mix with cold air in the upper troposphere.

While some contrails swiftly disappear, others form widespread cirrus clouds which block both the sun’s rays and heat energy from the ground. The effect is known as air induced cloudiness (AIC).

Today’s congested airways make it difficult to research AIC by comparing empty skies with those filled by aircraft.

Air travel is growing at an annual rate of between three per cent and five per cent for passenger aircraft and seven per cent for cargo flights.

In September 2001, US airspace was closed to commercial aircraft after the World Trade Centre terrorist attacks, offering scientists a chance to study what happened when aircraft contrails were suddenly absent. However, the results were not clear-cut.

The new research looked at the opposite effect, the impact of contrails on the normally empty skies of the 1940s.

Prof MacKenzie said: “This is tantalising evidence that Second World War bombing raids can be used to help us understand processes affecting contemporary climate. By looking back at a time when aviation took place almost entirely in concentrated batches for military purposes, it is easier to separate the aircraft-induced factors from all the other things that affect climate.”